The present invention relates to a tube type fluorescent lamp, in which prevention of blackening of tube ends provided with discharging electrodes is achieved and the same luminance as that on a general portion of the lamp is obtained also on ends of the lamp.
Conventionally, a straight tube type fluorescent lamp 50 shown in FIG. 4 is frequently used for illumination in an interior of a room, showcase, show window, or the like. The fluorescent lamp 50 of this kind is normally constructed such that caps 52 provided with two pins 53, 53 are provided on both ends of a glass tube 51 in the form of a straight tube. A fluorescent paint is coated on an inner wall surface of the glass tube 51, the interior of the tube is filled with mercury vapor as well as an inert gas such as argon gas or the like, discharging electrodes are provided at ends of the tube to be electrically connected to the pins 53, electrons emitted from the discharging electrodes strike against mercury vapor to produce electric discharge, and ultraviolet rays discharged excite the fluorescent paint to make the same emit light.
[Patent Document 1]
JP-A-63537
With fluorescent lamps, however, when lighting time elapses, there is caused a sputtering phenomenon, that is, a phenomenon that electrodes are gradually consumed and scattered to adhere to tube walls of a glass tube together with a charged substance, thereby blackening glass tube ends. Although such blackening phenomenon 54 shows signs of a service life of a concerned fluorescent lamp, a lighting fitting, in which a fluorescent lamp is arranged to be exposed directly outside, involves a problem that such blackening phenomenon worsens attractiveness.
Meanwhile, since a fluorescent lamp has a discharging characteristic to be increased in brightness from positions somewhat distant from discharging electrodes, tube ends darken relatively as compared with a general portion of the lamp. Further, since tube ends of a fluorescent lamp are provided with caps, dark portions increase. In connection with the problem that tube ends of a fluorescent lamp darken, Patent document 1 describes an invention of a fluorescent lamp, which comprises electron emitting portions for emitting electrons, and support portions supporting the electron emitting portions, the electron emitting portions and the support portions being arranged in the vicinity of ends of the fluorescent lamp and in which the support portions are bent toward the ends of the fluorescent lamp to make the electron emitting portions close to the ends, thus ensuring luminance on the end sides. Also, it is described that according to the invention, the support portions are bent toward the ends, whereby blackening of the ends of the fluorescent lamp is correspondingly suppressed.
Assuredly, although Patent document 1 describes the effect of suppressing blackening on the ends of the fluorescent lamp, blackening itself cannot be prevented and worsening of attractiveness is not still dissolved since blackening progresses with the lapse of time.